CN112238395A

CN112238395A - Chemical mechanical planarization tool

Info

Publication number: CN112238395A
Application number: CN202010542306.5A
Authority: CN
Inventors: 龚俊豪; 王上瑜; 蔡晴翔; 黄惠琪; 陈科维
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2019-07-18
Filing date: 2020-06-15
Publication date: 2021-01-19
Also published as: US11590627B2; US20230219188A1; US20210016415A1; TW202103853A

Abstract

A tool for performing chemical mechanical planarization includes holding a wafer by a retaining ring attached to a carrier, pressing the wafer against a first surface of a polishing pad, rotating the polishing pad at a first speed, dispensing a slurry onto the first surface of the polishing pad, and generating vibrations at the polishing pad.

Description

Chemical mechanical planarization tool

Technical Field

The present disclosure relates to a chemical mechanical planarization tool and a method for performing a chemical mechanical planarization process, and more particularly, to a chemical mechanical planarization tool for a wafer and a method for performing a chemical mechanical planarization process.

Background

Generally, a semiconductor device includes active components (transistors) formed on a substrate. Any number of interconnect layers (interconnects) may be formed over the substrate that connect the active elements to each other and to external devices. The interconnect layer is typically made of low-k dielectric materials (low-k dielectric materials) including metal trenches/vias.

As layers of the device are formed, planarization processes may be performed to planarize the layers to facilitate the formation of subsequent layers. For example, forming metal features in a substrate or in a metal layer may result in topography (topographies) that are not uniform. This non-uniform topography can create difficulties in the formation of subsequent layers. For example, the non-uniform topography may interfere with lithographic processes (photolithographic processes) that are typically used to form various features in the device. Thus, it may be advantageous to planarize the surface of the device after forming various features or layers.

Chemical Mechanical Polishing (CMP) is a common practice in the formation of integrated circuits. Typically, chemical mechanical polishing is used for planarization of semiconductor wafers. Chemical mechanical polishing utilizes a synergistic effect of physical and chemical forces (synergistic effect) to polish wafers. Chemical mechanical polishing is performed by applying a load force to the back side of the wafer while the wafer is resting on the polishing pad. The polishing pad is placed against the wafer. The polishing pad and wafer are then rotated as a slurry containing an abrasive and reactive chemicals passes therebetween. Chemical mechanical polishing is an effective method for achieving global planarization of a wafer.

Disclosure of Invention

It is an object of the present disclosure to provide a chemical mechanical planarization tool to address at least one of the above-mentioned problems.

Some embodiments of the present disclosure provide a chemical mechanical planarization tool, comprising: a carrier, a retaining ring, and a megasonic generator. The retaining ring is attached to the carrier and configured to hold a wafer during a chemical mechanical planarization process. The megasonic generator is attached to the carrier and configured to generate a plurality of vibrations during the chemical mechanical planarization process.

Some embodiments of the present disclosure provide a method of performing a chemical mechanical planarization process, comprising: rotating a polishing pad at a first rotational speed, dispensing a slurry onto a first surface of the polishing pad, pressing a wafer against the first surface of the polishing pad, the wafer being held by a retaining ring of a carrier, and generating vibrations on the polishing pad during a chemical mechanical planarization process using a megasonic generator.

Some embodiments of the present disclosure provide a method of performing a chemical mechanical planarization process, comprising: holding a wafer by a retaining ring attached to a carrier, pressing the wafer against a first surface of a polishing pad, the polishing pad rotating at a first speed, dispensing a slurry onto the first surface of the polishing pad, and generating vibrations at the polishing pad.

Drawings

Aspects of the disclosure are best understood from the following detailed description when read with the accompanying drawing figures. It should be noted that, in accordance with standard practice in the industry, the various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

Fig. 1 illustrates a perspective view of a chemical mechanical planarization apparatus in accordance with one embodiment.

Figure 2 illustrates a top view of the chemical mechanical planarization apparatus of figure 1, in accordance with one embodiment.

Figure 3 illustrates a cross-sectional view of the chemical mechanical planarization apparatus of figure 1, in accordance with one embodiment.

Fig. 4 illustrates an enlarged cross-sectional view of a polishing pad, a wafer, and a megasonic (megasonic) generator of the chemical mechanical planarization apparatus of fig. 1, in accordance with one embodiment.

Figure 5 illustrates a control voltage provided to a megasonic generator of the chemical mechanical planarization apparatus of figure 1, in accordance with one embodiment.

Fig. 6 illustrates a control voltage supplied to a megasonic generator of the chemical mechanical planarization apparatus of fig. 1, in accordance with another embodiment.

Fig. 7 illustrates a control voltage supplied to a megasonic generator of the chemical mechanical planarization apparatus of fig. 1 in accordance with yet another embodiment.

Figure 8 illustrates a flow diagram of a method for performing a chemical mechanical planarization process, in accordance with some embodiments.

The reference numbers are as follows:

100 chemical mechanical planarization apparatus

105 platform

106 shaft

115 polishing pad

115H cavity

115P peak

116 opening of the container

120 abrasive head

125 vector

127 holding ring

130 pad conditioner arm

135 pad regulator head

137 pad regulator

140 slurry distributor

150: slurry

200: point

215 double-headed arrow

220 point

225 double-headed arrow

230: point

235 double-headed arrow

237 double-headed arrow

300 wafer

305 bottom layer

307 overlying layer

310 film

320 megasonic generator

321 holder

323 piezoelectric transducer

325 electric terminal

327 shaft

331 power supply

333 output terminal

335 controller

340 conducting wire

410 abrasive

610A control voltage pulse

610B control voltage pulse

610C control voltage pulse

610D control voltage pulse

610E control voltage pulse

1000 method

1010 step

1020 step of

1030 step (b)

1040 step (1)

T0 time

T1 time

T2 time

T_ADuration of time

T_BDuration of time

Vt control voltage

X is the X axis

Y is the Y axis

Z is the Z axis

Detailed Description

The following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

Furthermore, spatially relative terms, such as "below," "under," "above," "on," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature as illustrated. Spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Embodiments of the present disclosure relate to Chemical Mechanical Planarization (CMP) tools and processes, and in particular, to CMP tools and processes that use megasonic generators during CMP processes to generate vibrations in the polishing pad to reduce abrasive accumulation. In some embodiments, the mode of vibration, such as the frequency of vibration, the amplitude of vibration, and/or the duration of vibration, is varied during the chemical mechanical planarization process to achieve a target wafer polishing profile. Improved planarity and etch rate of a chemical mechanical planarization process is thus achieved using the disclosed chemical mechanical planarization tools and processes. Additional advantages include reduced polishing pressure to push the wafer onto the polishing pad, which reduces wafer damage.

Chemical mechanical planarization is a method of planarizing features created in the manufacture of semiconductor devices. The process combines the use of polishing materials in a reactive chemical slurry with a polishing pad. The polishing pad typically has a larger diameter than the semiconductor wafer. In a chemical mechanical planarization process, the polishing pad and the wafer are pressed together. This process removes material and tends to homogenize the irregular topography, thereby making the wafer flat or substantially flat. This prepares the wafer for the formation of additional overlying circuit elements. For example, chemical mechanical planarization can bring the entire wafer surface within a given depth of field (depth of field) of the lithography system. A typical specification for depth of field is on the order of, for example, angstroms (angstroms). In some embodiments, chemical mechanical planarization may also be employed to selectively remove material based on its location on the wafer.

In a chemical mechanical planarization process, a wafer is placed in a carrier head (also referred to as a carrier), where it is held in place by a retaining ring (retainer ring). The carrier head and wafer are then rotated while downward pressure is applied to the wafer to press against the polishing pad. A reactive chemical solution is dispensed on the contact surface of the polishing pad to aid in planarization. The surface of the wafer can thus be planarized using a combination of mechanical and chemical mechanisms.

Figure 1 illustrates a perspective view of a chemical mechanical planarization apparatus 100, in accordance with some embodiments. The chemical mechanical planarization apparatus 100 includes a platen 105 and a polishing pad 115 (e.g., glued) over the platen 105. In some embodiments, the abrasive pad 115 comprises a single layer or composite layer of material (e.g., felt (felts), polymer impregnated felt (polymer impregnated felts), microporous polymer films (microporous polymer films), microporous synthetic leathers (microporous synthetic leathers), filled polymer films (filled polymer films), unfilled textured polymer films (unfilled textured polymer films), combinations thereof, and the like). Representative polymers include polyurethane (polyurethane), polyolefin (polyurethane), and the like.

As shown in fig. 1, a polishing head 120 (which may also be referred to as a polishing head) is placed on the polishing pad 115. The grinder head 120 includes a carrier 125, a retaining ring 127, and a megasonic generator 320. The retaining ring 127 and megasonic generator 320 are mounted to the carrier 125 using mechanical fasteners (e.g., screws, etc.) or other suitable attachment means. In the example of fig. 1, the retaining ring 127 is attached to the lower side of the carrier 125 and the megasonic generator 320 is attached to the upper side of the carrier 125. The megasonic generator 320 may include a piezoelectric transducer (PZT) and be configured to generate vibrations at the carrier 125 and at the polishing pad 115 during a chemical mechanical planarization process. More details regarding the megasonic generator 320 are discussed below.

During a representative chemical mechanical planarization process, a workpiece (e.g., a semiconductor wafer; not shown in fig. 1, but illustrated and described below with respect to fig. 3) is placed within carrier 125 and held by retaining ring 127. In some embodiments, the retaining ring 127 has a substantially annular shape with a substantially hollow center. The workpiece is placed in the center of the retaining ring 127 such that the retaining ring 127 holds the workpiece in place during the chemical mechanical planarization process. The workpiece is positioned such that the surface to be polished faces in a direction toward the polishing pad 115 (e.g., downward). The carrier 125 is configured to apply a downward force or pressure to urge the workpiece into contact with the polishing pad 115. During the chemical mechanical planarization process, the abrasive head 120 is configured to rotate the workpiece over the polishing pad 115 to impart a mechanical polishing action to affect the contact surface of the workpiece or planarize polishing.

In some embodiments, the chemical mechanical planarization apparatus 100 includes a slurry dispenser 140 configured to deposit a slurry 150 onto the polishing pad 115. The platform 105 is configured to rotate, causing slurry 150 to be dispensed between the workpiece and the platform 105 through a plurality of grooves in the retaining ring 127. The plurality of grooves may extend from an outer sidewall of the retaining ring 127 to an inner sidewall of the retaining ring 127.

The composition of the slurry 150 may depend on what type of material is to be ground or removed. For example, the slurry 150 may include reactants, abrasives, surfactants, and solvents. The reactant may be a chemical species, such as an oxidizing agent or a hydrolyzing agent (hydrosizer), that chemically reacts with the material of the workpiece to assist the polishing pad 115 in polishing or removing material. In some embodiments where the material to be removed includes, for example, tungsten, the reactant may be, for example, hydrogen peroxide, dichromate (Cr)₂O₇) Permanganic acid (MnO)₄) Osmium tetroxide (OsO)₄) (ii) a Although other suitable reactants may be used, alternately, in combination, in succession, such as hydroxylamine (hydroxyimine), periodic acid (periodate acid), other periodates (periodates), iodates (ioates), ammonium persulfate (ammonium persulfate), peroxymonosulfates (peroxomonosulfates), peroxymonosulfuric acid (peroxomonosulfuric acid), perborates (perborates), malonamide (malonamide), combinations thereof, and the like. In other embodiments, other reactants may be used to remove other types of materials. For example, in embodiments where the material to be removed includes, for example, an oxide, the reactant may include, for example, nitric acid (HNO)₃) Potassium hydroxide (KOH), ammonium hydroxide (NH)₄OH), combinations thereof, and the like.

The abrasive can include any suitable particles configured to abrade or planarize the workpiece in conjunction with the relative mechanical motion of the abrasive pad 115. In some embodiments, the abrasive comprises colloidal alumina (aluminum oxide). In some embodiments, the abrasive comprises silicon oxide (silica oxide), aluminum oxide (alumina oxide), cerium oxide (cerium oxide), polycrystalline diamond (polycrystalline diamond), polymeric particles (e.g., polymethacrylate), and the like), combinations thereof, and the like.

Surfactants can be used to help disperse the reactants and abrasives within the slurry 150 and to prevent (or reduce the occurrence of) aggregation of the abrasives during the chemical mechanical planarization process. In some embodiments, the surfactant may include polyethylene glycol (PEG), polyacrylic acid (polyacrylic acid), sodium salts of polyacrylic acid (sodium salts of polyacrylic acid), potassium oleate (potassium oleate), sulfosuccinates (sulfosuccinates), sulfosuccinate derivatives (sulfosuccinate derivatives), sulfonated amines (sulfonated amines), sulfonated amides (sulfonated amides), sulfates of alcohols (sulfonates), alkyl sulfonates (alkyl sulfonates), carboxylated alcohols (carboxylated amides), alkyl aminopropionic acids (alkylated aminopropionic acids), alkyl imino acids (alkylated aminopropionic acids), combinations thereof, and the like. However, such representative examples are not intended to be limited to the listed surfactants. One skilled in the art will appreciate that any suitable surfactant may be used instead, in combination, or sequentially.

In some embodiments, the slurry 150 includes a solvent that can be used to bind the reactants, abrasive, and surfactant, and allow this mixture to move and disperse onto the polishing pad 115. In some embodiments, the solvent includes, for example, deionized water (DIW), an alcohol, or an azeotrope thereof; however, other suitable solvents may be used alternately, in combination, or continuously.

In addition, other additives may be added, if desired, to help control or otherwise benefit the chemical mechanical planarization process. For example, corrosion inhibitors may be added to help control corrosion. In a particular embodiment, the corrosion inhibitor may be an amino acid (amino acid) such as glycine (glycine). However, any suitable corrosion inhibitor may be used.

In another embodiment, a chelating agent is added to the slurry 150. The chelating agent may be an agent (agent) such as ethylenediaminetetraacetic acid (EDTA), C₆H₈O₇、C₂H₂O₄Combinations thereof, and the like. However, any suitable chelating agent may be used.

In yet another embodiment, the slurry 150 includes a pH adjuster to control the pH of the slurry 150. For example, hydrochloric acid (HCl), nitric acid (HNO), for example, may be used₃) Phosphoric acid (H)₃PO₄) Maleic acid (C2H)₂(COOH)₂) Potassium hydroxide (KOH), ammonia (NH)₄OH), combinations thereof, and the like, is added to the slurry 150 to adjust the pH of the slurry 150 up or down.

In addition, other additives may be added to help control and manage the chemical mechanical planarization process. For example, down-force enhancer (e.g., organic compounds), grinding rate inhibitors, and the like may also be added. Any suitable additive that may be useful to the grinding process may be used and all such additives are fully intended to be included within the scope of the embodiments.

In some embodiments, chemical mechanical planarization apparatus 100 includes a pad conditioner 137 attached to a pad conditioner head 135. The pad conditioner head 135 is configured to rotate a pad conditioner 137 over the polishing pad 115. Pad conditioner 137 is mounted to pad conditioner head 135 using mechanical fasteners (e.g., screws, etc.) or by other suitable attachment means. Pad conditioner arm 130 is attached to pad conditioner head 135 and is configured to move pad conditioner head 135 and pad conditioner 137 in a motion that sweeps across the area of polishing pad 115. In some embodiments, pad conditioner head 135 is mounted to pad conditioner arm 130 using mechanical fasteners (e.g., screws, etc.) or by other suitable attachment means. Pad conditioner 137 includes a substrate having a plurality of abrasive particles bonded thereto. The pad conditioner 137 removes accumulated wafer debris and excess slurry 150 from the polishing pad 115 during the chemical mechanical planarization process. In some embodiments, the pad conditioner 137 also acts as an abrasive for the polishing pad 115 to refresh the workpiece being polished, or to create a desired texture (such as, for example, grooves, etc.).

As shown in fig. 1, the chemical mechanical planarization apparatus 100 has a single abrasive head (e.g., 120) and a single polishing pad (e.g., 115). However, in other embodiments, the chemical mechanical planarization apparatus 100 can have multiple polishing heads or multiple polishing pads. In some embodiments where the chemical mechanical planarization apparatus 100 has multiple abrasive heads and a single polishing pad, multiple workpieces (e.g., semiconductor wafers) can be polished simultaneously. In other embodiments where the chemical mechanical planarization apparatus 100 has a single abrasive head and multiple polishing pads, the chemical mechanical planarization process may include a multi-step process. In such embodiments, a first polishing pad may be used to remove bulk material from the wafer, a second polishing pad may be used for global planarization of the wafer, and a third polishing pad may be used, for example, to polish (buff) the surface of the wafer. In some embodiments, different slurry compositions may be used at different stages of the chemical mechanical planarization process. In yet other embodiments, all chemical mechanical planarization stages may use the same slurry composition.

Fig. 2 illustrates a top view (or plan view) of the chemical mechanical planarization apparatus 100 of fig. 1, in accordance with some embodiments. The platen 105 (located below the polishing pad 115 of fig. 2) is configured to rotate in either a clockwise or counterclockwise direction (indicated by double-headed arrow 215 about an axis extending through the centrally-located point 200, which is the center point of the platen 105). The grinder head 120 is configured to rotate in either a clockwise or counterclockwise direction (indicated by double-headed arrow 225 about an axis extending through point 220, which is the center point of the grinder head 120). The axis through point 200 is parallel to the axis through point 220. In the illustrated embodiment, the axis passing through point 200 is spaced from the axis passing through point 220. Pad conditioner head 135 is configured to rotate in either a clockwise or counterclockwise direction (indicated by double-headed arrow 235 about an axis extending through point 230, which is the center point of pad conditioner head 135). The axis through point 200 is parallel to the axis through point 230. Pad conditioner arm 130 is configured to move pad conditioner head 135 across the surface of polishing pad 115 (e.g., as indicated by double-headed arrow 237) during rotation of platen 105.

As feature sizes continue to shrink in advanced semiconductor process generations (advanced semiconductor processing nodes), the requirements for planarity of various layers on a wafer become more stringent. In some advanced technology generations (advanced technology nodes), nano-sized abrasives are used in slurries for chemical mechanical planarization processes. The nano-sized abrasive (also referred to as nanoparticles, or nano-abrasive particles) can have a size (e.g., diameter) of less than about 30 nanometers (nm), such as between about 3 nanometers and about 5 nanometers. A slurry using nano abrasive particles is also referred to as a nano abrasive slurry. Conversely, it is known that the size (e.g., diameter) of the abrasive in slurries can be greater than 35 nanometers, such as between about 50 nanometers and about 100 nanometers.

Although chemical mechanical planarization processes using nanoabrasive slurries can achieve better planarity, many challenges remain. For example, if a chemical mechanical planarization process is performed by merely replacing a conventional slurry with a nano-abrasive slurry, the etch rate (also referred to as the removal rate) of a chemical mechanical planarization process using a nano-abrasive slurry may be very slow, such as less than 200 angstroms per minute. Due to the long chemical mechanical planarization process time required, it may be impractical to use such slow etch rates in fabrication. To compensate for the slow etch rate using a nano-abrasive slurry, known chemical mechanical planarization processes may have to increase the force/pressure used to press the wafer against the polishing pad 115 (which may be referred to as the polishing pressure below for ease of discussion), or increase the flow rate of the slurry used in the chemical mechanical planarization process. However, increasing the grinding pressure may increase the risk of wafer damage, such as scratches or fractures on the wafer. Increasing the polishing pressure may also make it difficult for slurry to flow between the polishing pad 115 and the wafer, which may lead to undesirable performance of the polishing process. In addition, increasing the flow rate of the slurry also increases the loss of the slurry, which increases the manufacturing cost.

Another challenge of chemical mechanical planarization processes using nano-abrasive slurries is abrasive clustering, which means that the abrasive in the slurry is not uniformly distributed over the entire surface of the polishing pad 115, and may be clustered in certain locations, such as in the openings 116 (see fig. 4) at the upper surface of the polishing pad 115.

Referring briefly to fig. 4, a cross-sectional view of (a portion of) the polishing pad 115, the wafer 300, and the megasonic generator 320 is shown. As shown in fig. 4, the polishing pad 115 may be porous and may have a cavity 115H therein. The opening 116 may be formed at least in part by a cavity exposed at the upper surface of the polishing pad 115. Fig. 4 also shows an abrasive 410 used in the slurry, which abrasive 410 may collect in the openings 116, rather than on the top surface (e.g., the raised portion at the upper surface) of the peaks 115P of the polishing pad 115. During the chemical mechanical planarization process, the abrasive 410 in the opening 116 may not contact the wafer 300 and thus is not functional, which reduces the efficiency of the slurry and results in a reduced etch rate in the chemical mechanical planarization process. On the other hand, if abrasive 410 collects at certain locations at the top surface of peaks 115P, these locations may be over-etched (off), which may result in localized dishing (dishing) on the surface of wafer 300. Various embodiments discussed herein achieve improved etch rates and better surface planarity for chemical mechanical planarization processes by preventing or reducing abrasive accumulation using megasonic generator 320. Furthermore, the disclosed embodiments allow for the use of lower polishing pressures and lower slurry flow rates in chemical mechanical planarization processes, thereby reducing the risk of wafer damage and reducing manufacturing costs, the details of which are discussed below.

Referring now to fig. 3, a cross-sectional view of the chemical mechanical planarization apparatus 100 of fig. 1 is shown, in accordance with an embodiment. It should be noted that not all features of the chemical mechanical planarization apparatus 100 are shown in figure 3 for clarity. As shown in fig. 3, the platen 105 (with the polishing pad 115 attached thereto) rotates about the shaft 106. The grinder head 120 includes a carrier 125, a retaining ring 127, and a megasonic generator 320, and rotates about an axis 327. The platen 105 and the grinder head 120 may rotate in the same direction or in opposite directions.

In the example of fig. 3, carrier 125 includes a thin film (membrane)310 configured to interface with wafer 300 during a chemical mechanical planarization process. In some embodiments, the chemical mechanical planarization apparatus 100 includes a vacuum system coupled to the grinder head 120, and the membrane 310 is configured to pick up and hold the wafer 300 on the membrane 310 using, for example, vacuum suction. The membrane 310 may form an enclosed space by itself or with the underside of the carrier 125. During the chemical mechanical planarization process, the pressure within the enclosed space (which may also be referred to as the internal pressure of the membrane) may be maintained at a predetermined level such that the expanding membrane 310 pushes the wafer 300 down toward the polishing pad 115. By adjusting the internal pressure of the membrane 310, the grinding pressure can be adjusted.

Still referring to fig. 3, the megasonic generator 320 includes a holder 321, electrical terminals (electrical terminals)325, and piezoelectric transducers (PZT) 323. A holder 321 may be used to hold the piezoelectric transducer 323 and attach the megasonic generator 320 to the shaft 327. The holder 321 may also include circuitry to electrically couple the electrical terminals 325 with the piezoelectric transducer 323. A control voltage Vt for controlling the operation of the piezoelectric transducer 323 is applied to the electrical terminal 325 through the power source 331 to generate vibration. The power supply 331 may include a controllable voltage source and a power amplifier to generate a control voltage Vt at an output terminal 333. The control voltage at the output terminal 333 of the power supply 331 is then provided to the electrical terminal 325 through a wire 340 (e.g., a copper wire). In some embodiments, the wires 340 are routed through the interior of the shaft 327 (which may be hollow) to connect with the power source 331.

Fig. 3 further illustrates a controller 335 electrically coupled to the power source 331. The controller 335 may direct and control the power supply 331 to generate control voltages having different parameters to generate different vibration modes through the piezoelectric converter 323, the details of which are discussed below with reference to fig. 5-7. In some embodiments, the power supply 331 and the controller 335 are external to the megasonic generator 320 and therefore are not part of the megasonic generator 320. In some embodiments, the power supply 331 and the controller 335 are integrated into the megasonic generator 320 and are thus part of the megasonic generator 320.

As shown in fig. 3, the piezoelectric transducer 323 is attached to the carrier 125. During the chemical mechanical planarization process, when a control voltage Vt is applied to the piezoelectric transducer 323, the movement of the piezoelectric transducer 323 generates vibrations that are transmitted through physical contact or other transmission media (e.g., slurry) to, for example, the carrier 125, the retaining ring 127, and the polishing pad 115. The vibrations generated by the megasonic generator 320 can be along a first direction in a plane parallel to the upper surface of the polishing pad 115 (e.g., a plane defined by the X-axis and the Y-axis in fig. 1), along a second direction perpendicular to the upper surface of the polishing pad 115 (e.g., along the Z-axis in fig. 1), or along both the first direction and the second direction. Although the megasonic generator 320 is shown in fig. 3 as being mounted on the carrier 125 and rotating about the axis 327, other configurations or locations of the megasonic generator 320 are possible and are fully intended to be included within the scope of the present disclosure. For example, the megasonic generator 320 may be mounted at a lower surface of the platform 105 and may rotate about the axis 106.

In some embodiments, wafer 300 is a semiconductor wafer that includes, for example, a semiconductor substrate (e.g., comprising silicon, III-V semiconductor materials, etc.), active devices (e.g., transistors, etc.) formed in or on the semiconductor substrate, and various interconnect structures. Representative interconnect structures may include conductive features that electrically connect active devices to form functional circuits. In various embodiments, a chemical-mechanical planarization process may be applied to the wafer 300 during any stage of fabrication to planarize features or otherwise remove material (e.g., dielectric materials, semiconductor materials, conductive materials, etc.) of the wafer 300. The wafer 300 may include any subset of the features identified above, as well as other features.

As shown in fig. 3, wafer 300 includes a bottommost layer 305 and an overlying layer 307. During the chemical mechanical planarization process, the bottom-most layer 305 is polished/planarized. In some embodiments, the bottom-most layer 305 comprises a metal, such as tungsten, copper, cobalt, titanium, ruthenium, combinations thereof, and the like. In some embodiments, the bottom-most layer 305 comprises a dielectric material, such as silicon oxide, silicon nitride, combinations thereof, and the like. In some embodiments, the bottom-most layer 305 comprises a semiconductor material, such as silicon, polysilicon, silicon germanium, silicon carbide, combinations thereof, and the like. The bottom-most layer 305 may be polished to form contact plugs (contact plugs) that contact various active devices of the wafer 300, for example. In embodiments where the bottom-most layer 305 includes copper, the bottom-most layer 305 may be ground to form various interconnect structures, such as the wafer 300. In embodiments where the bottom-most layer 305 comprises a dielectric material, the bottom-most layer 305 may be polished to form, for example, a Shallow Trench Isolation (STI) structure on the wafer 300.

In some embodiments, the bottom-most layer 305 may have a non-uniform thickness (e.g., exhibit local or global topographical variations of the exposed surface of the bottom-most layer 305) due to process variations experienced during deposition of the bottom-most layer 305. For example, in embodiments where the lowermost layer 305 to be planarized comprises tungsten, the lowermost layer 305 may be formed by depositing tungsten into openings through the dielectric layer using a Chemical Vapor Deposition (CVD) process. The bottom-most layer 305 may have a non-uniform thickness due to variations in the chemical vapor deposition process or other underlying structures.

In some embodiments, the thickness profile of the bottommost layer 305 may be measured using ellipsometry (ellipsometry), interferometry (interferometry), reflectometry (reflectometry), picosecond ultrasound (picosecond ultrasound), Atomic Force Microscopy (AFM), Scanning Tunneling Microscopy (STM), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and the like. In some embodiments, a thickness measurement device (not shown) may be external to the chemical mechanical planarization device 100 and may measure or otherwise determine the thickness profile of the bottom-most layer 305 prior to loading the wafer 300 into the chemical mechanical planarization device 100. In other embodiments, the thickness measurement device may be part of the chemical mechanical planarization device 100 and may measure or otherwise determine the thickness profile of the bottom-most layer 305 after the wafer 300 is loaded into the chemical mechanical planarization device 100.

After the measurement, the bottom-most layer 305 may be planarized by the chemical mechanical planarization apparatus 100. In certain embodiments, the grinder head 120 may be lowered such that the bottom most layer 305 of the wafer 300 is in physical contact with the polishing pad 115. In addition, slurry 150 is also introduced onto polishing pad 115 such that slurry 150 will contact the exposed surface of bottommost layer 305. For example, the slurry 150 may be introduced at a flow rate between about 100 cubic centimeters per minute (cc/min) and about 500 cubic centimeters per minute (e.g., about 250 cubic centimeters per minute). The surface of the wafer 300 (e.g., the bottom most layer 305) can thus be planarized using a combination of mechanical and chemical forces.

Referring now to fig. 4, an enlarged cross-sectional view of a portion of the polishing pad 115, a portion of the wafer 300, and a portion of the megasonic generator 320 is shown. The vibrations generated by the megasonic generator 320 help to evenly distribute the abrasive 410 across the upper surface of the polishing pad 115 during the cmp process. For example, some of the abrasives 410 that collect at the bottom of the openings 116 (e.g., between adjacent peaks 115P) may be vibrationally stirred and distributed to the top surface of the peaks 115P (e.g., between the peaks 115P and the wafer 300), thus becoming effective abrasives 410 that participate in the lapping process. Thus, the etch rate of the chemical mechanical planarization process may reach, for example, 3000 angstroms per minute or more for an oxide film, which may be 10% to 20% better than a chemical mechanical planarization process that does not use the megasonic generator 320. The even distribution of the abrasive 410 also reduces local dishing effects, thus achieving better planarity of the abraded wafer surface.

In some embodiments, the frequency of the vibrations generated by the megasonic generator 320 is between about 10 kilohertz (KHz) to about 50 KHz (which may be the same or proportional to the frequency of the control voltage Vt). Vibration frequencies less than 10 khz may be too low to be effective in reducing abrasive agglomeration. However, vibration frequencies greater than 50 khz may be too high and may damage the wafer 300 (e.g., may damage the surface of the wafer 300).

In some embodiments, the platen 105 rotates at a speed of between about 30 revolutions per minute (rpm) and about 120 rpm, and the grinder head 120 rotates at a speed of between about 30 revolutions per minute and about 120 revolutions per minute. If the rotational speed of the platen 105 and the grinder head 120 is below about 30 revolutions per minute, the rotational speed may be too low and the effects of vibration may be limited to localized areas of the wafer surface for too long and may result in non-uniform etch rates at different localized areas of the wafer surface. For example, the abrasives 410 may be stirred up from the bottom of the openings 116, but may not be distributed quickly to other areas, which may result in local surface areas having a higher abrasive concentration than other local surface areas with fewer openings 116. Therefore, the etch rate may be different in different local areas and may result in non-uniform etch rates. On the other hand, if the rotational speed of the platen 105 and the grinder head 120 is greater than about 120 revolutions per minute, the effectiveness of the slurry may be reduced. This may be due to the fresh slurry being dispersed too quickly over the pad surface, which may result in a very thin layer of fresh slurry, thereby reducing the etch rate of the chemical mechanical planarization process.

In some embodiments, the polishing pad 115 has a porosity (porosity) of between about 10% and about 80%, such as between about 30% and about 60%, or between about 40% and about 50%. For polishing pads 115 with lower porosity (e.g., less than 10%), the benefit of the megasonic generator 320 may not be significant enough to justify the cost of the megasonic generator 320, since very little abrasive accumulates in the openings 116. If the porosity is too high (e.g., greater than 80%), the effectiveness of the megasonic generator 320 may be limited. This is because with a high concentration of openings 116 at the upper surface of the polishing pad 115, the total area of the top surface of the peak 115P (where the effective abrasive 410 resides during the chemical mechanical planarization process) is too limited. In other words, the inactive abrasive particles 410, stirred up from the bottom of an opening 116 by the vibration, may fall back into another opening 116, and thus remain inactive abrasive particles.

Because of the improved etch rate achieved by the disclosed embodiments, there is no need to increase the flow rate of the slurry and the grinding pressure. In some embodiments, the flow rate of the slurry is between about 100 cubic centimeters per minute to about 500 cubic centimeters per minute, such as about 250 cubic centimeters per minute. The low flow rate of the slurry allowed by the present disclosure reduces manufacturing costs associated with slurry consumption. In some embodiments, due to the low polishing pressures allowed by the present disclosure, the internal pressure of the membrane 310 may be set between about 0.5 pounds-force per square inch (psi) to about 3 pounds-force per square inch during the chemical mechanical planarization process, which is lower than the range between about 1 to about 5 pounds-force per square inch for known chemical mechanical planarization processes without the megasonic generator 320. Lower grinding pressures reduce wafer damage. In addition, the use of the megasonic generator 320 in a chemical mechanical planarization process also achieves better surface planarity than known chemical mechanical planarization processes. For example, the topography (e.g., non-uniformity) of the ground wafer surface using the disclosed embodiments is about 10% to about 50% of the topography of the ground wafer surface using conventional chemical mechanical planarization processes.

In one embodiment, fig. 5 illustrates the control voltage provided to the megasonic generator 320. The X-axis of fig. 5 represents time, while the Y-axis represents amplitude. The control voltage of fig. 5 is a continuous wave (e.g., sine wave or cosine wave) signal having a predetermined frequency (e.g., about 10 kilohertz to about 50 kilohertz). In the illustrated embodiment, the frequency of the control voltage is the same as or proportional to the frequency of vibration of the megasonic generator 320. In some embodiments, the frequency of the control voltage is adjusted to achieve the target polishing surface profile after the chemical mechanical planarization process. Recall that the thickness profile of the bottom-most layer 305 of the wafer 300 can be measured prior to the chemical mechanical planarization process. The measured thickness profile of the bottom-most layer 305 can be used to determine, for example, the frequency of the control voltage of the megasonic generator 320. In some embodiments, the amplitude of the control voltage is adjusted to achieve a target polishing surface profile after the chemical mechanical planarization process. In some embodiments, both the frequency and amplitude of the control voltage are adjusted to achieve the target polishing surface profile after the chemical mechanical planarization process.

Fig. 6 shows the control voltage provided to the megasonic generator 320 in another embodiment. The X-axis of fig. 6 represents time, while the Y-axis represents amplitude. The control voltage in fig. 6 includes control voltage pulses (e.g., 610A, 610B), where each control voltage pulse includes one or more continuous wave control voltage cycles (e.g., periods) that are the same as or similar to the control voltage of fig. 5. For example, each control voltage pulse may have a duration between about 1 millisecond (ms) and about 300 ms. In some embodiments, each control voltage pulse has a first frequency and generates vibrations at the megasonic generator 320 at a second frequency, wherein the second frequency is the same as or proportional to the first frequency.

In the example of fig. 6, the amplitude, frequency, and/or duration of each control voltage pulse (e.g., 610A, or 610B) may be independently adjusted to achieve the target polishing surface profile, and thus differ from the amplitude, frequency, and/or duration of another control voltage pulse. As shown in fig. 6, each control voltage pulse is separated from adjacent control voltage pulses by a silent period (e.g., a period of no control voltage or zero control voltage, which corresponds to no vibration being generated at the megasonic generator 320). In some embodiments, the duration between adjacent control voltage pulses may be adjusted individually (e.g., see T in fig. 6)_AAnd T_B) And thus are different from each other. In the example of fig. 6, the control voltage may include control voltage pulses (e.g., 610A, 610C, 610D) having large amplitudes and control voltage pulses (e.g., 610B, 610E) having small amplitudes interspersed between the control voltage pulses having large amplitudes. Each control voltage pulse (e.g., 610A, 610C, or 610D) having a large amplitude may have a deviation in its amplitude (e.g., a non-zero average value), and thus, may include one or more continuous wave control voltage cycles that oscillate about the non-zero average value. For example, control voltage 610A has a positive offset, while control voltage 610C has a negative offset. Additionally, in some embodiments, a control voltage pulse (e.g., 610A, 610C, or 610D) having a large amplitude may have alternating positive and negative values (e.g., positive or negative) for its deviation. Control of fig. 6 each having a small amplitudeThe voltage pulses (e.g., 610B, 610E) may have a zero average value, or may have a small positive or negative deviation, e.g., less than 10% of the deviation of the large control voltages (e.g., 610A, 610C, 610D). The pattern of control voltages shown in fig. 6 is a non-limiting example only, other patterns are possible and are fully intended to be included within the scope of the present disclosure.

The control voltage shown in figure 6 has many degrees of freedom in the trim cmp process to achieve the target polishing surface profile. Those skilled in the art will appreciate that although the above discussion describes adjusting each control voltage pulse individually, in embodiments some or all of the control voltage pulses share the same parameters (e.g., the amplitude, frequency, duration of each control voltage pulse, and/or the duration between adjacent control voltage pulses) are fully intended to be included within the scope of the present disclosure.

Figure 7 illustrates a control voltage of another embodiment in which the control voltage is dynamically changed at different stages of the chemical mechanical planarization process. The X-axis of fig. 7 represents time, while the Y-axis represents frequency. In the illustrated embodiment, the frequency of the control voltage is the same as or proportional to the frequency of the vibrations at the megasonic generator 320. In FIG. 7, between time T0 and T1, the chemical mechanical planarization process is in a ramp-up stage and the frequency of the control voltage is increased in preparation for entering the main polishing stage of the chemical mechanical planarization process. Between time T1 and time T2, the cmp process is in a main polishing phase in which the wafer is polished at a relatively high etch rate using a first control voltage frequency (e.g., between about 20 khz and about 26 khz). Between time T2 and time T3, the chemical mechanical planarization process proceeds to a polish grind step, wherein the wafer is polished at a slower etch rate using a second control voltage frequency (e.g., between about 5 khz and about 15 khz) that is less than the frequency of the first control voltage. After time T3, the chemical mechanical planarization process enters a de-chuck (de-chuck) stage where the wafer is ready to be removed from the retaining ring 127. A third control voltage frequency (e.g., less than 4 khz) is used during the desorption stage, which may be less than the second control voltage frequency. The example of fig. 7 further illustrates a temporary decrease in the third control voltage frequency after a time T3 (e.g., about 3 to 5 seconds) before the third control voltage frequency settles at about 4 kilohertz. A temporary reduction (e.g., at a control voltage frequency of about 2 khz) may be performed to conform to the (accommodate) polishing head, which may be unstable at the beginning of the desorptive phase.

Embodiments may realize advantages. For example, megasonic generators reduce slurry accumulation and help distribute the slurry uniformly along the surface of the polishing pad, thereby increasing the etch rate of the cmp process and achieving better planarity of the polished wafer surface. The disclosed chemical mechanical planarization tool allows for the application of low polishing pressures (e.g., between about 0.5 pound-force per square inch to about 3 pound-force per square inch) to the wafer, thereby reducing the risk of wafer damage associated with large polishing pressures. The flow rate of the slurry used in the chemical mechanical planarization process can be kept low compared to known chemical mechanical planarization processes, which saves manufacturing costs associated with slurry consumption. Although the present disclosure is discussed using the example of a nano-abrasive slurry, the disclosed embodiments may be applied to chemical mechanical planarization processes using abrasives having other dimensions (e.g., diameters between 2 nanometers to about 300 nanometers).

Fig. 8 illustrates a flow diagram of a method 1000 for performing a chemical mechanical planarization process, in accordance with some embodiments. It should be understood that the embodiment method shown in FIG. 8 is merely exemplary of many possible embodiment methods. Those skilled in the art will recognize many variations, substitutions, and modifications. For example, various steps shown in FIG. 8 may be added, removed, replaced, rearranged, and repeated.

Referring to fig. 8, in step 1010, the wafer is held by a retaining ring attached to a carrier. In step 1020, the wafer is pressed against a first surface of the polishing pad, rotating the polishing pad at a first speed. In step 1030, a slurry is dispensed on a first surface of a polishing pad. In step 1040, vibration is generated at the polishing pad.

According to some embodiments of the present disclosure, there is provided a chemical mechanical planarization tool, comprising: a carrier, a retaining ring, and a megasonic generator. The retaining ring is attached to the carrier and configured to hold a wafer during a chemical mechanical planarization process. The megasonic generator is attached to the carrier and configured to generate a plurality of vibrations during the chemical mechanical planarization process.

In one embodiment, the megasonic generator includes a piezoelectric transducer. In one embodiment, the megasonic generator is configured to generate vibrations having a frequency between about 10 kilohertz and about 50 kilohertz. In one embodiment, the megasonic generator is configured to generate vibrations in a direction within a plane parallel to a major surface of the wafer or in a direction perpendicular to the major surface of the wafer. In one embodiment, the chemical mechanical planarization tool further comprises: a platen and a polishing pad. A polishing pad is attached to an upper surface of the platen, wherein the carrier is configured to press the wafer against the polishing pad during the chemical mechanical planarization process. In one embodiment, the polishing pad has a porosity of about 10% to about 80%. In one embodiment, the chemical mechanical planarization tool further comprises a slurry dispenser configured to dispense a slurry onto the polishing pad during a chemical mechanical planarization process, wherein one of the plurality of abrasives in the slurry has a diameter of less than about 30 nanometers.

According to further embodiments of the present disclosure, there is provided a method of performing a chemical mechanical planarization process, comprising: rotating a polishing pad at a first rotational speed, dispensing a slurry onto a first surface of the polishing pad, pressing a wafer against the first surface of the polishing pad, the wafer being held by a retaining ring of a carrier, and generating vibrations on the polishing pad during a chemical mechanical planarization process using a megasonic generator.

In one embodiment, the first rotation speed is between about 30 revolutions per minute and about 120 revolutions per minute, wherein the method further comprises rotating the wafer at a second rotation speed between about 30 revolutions per minute and about 120 revolutions per minute. In one embodiment, the operation of generating vibrations includes generating vibrations having a frequency between about 10 kilohertz and about 50 kilohertz using a megasonic generator. In one embodiment, the polishing pad has a porosity of about 10% to about 80%. In one embodiment, one of the plurality of abrasives in the slurry has a diameter of less than about 30 nanometers. In one embodiment, the operation of dispensing the slurry includes dispensing the slurry onto the first surface of the polishing pad during the chemical mechanical planarization process at a flow rate between about 0.1 liters per minute and about 0.5 liters per minute. In one embodiment, the carrier includes a membrane that contacts the wafer during the chemical mechanical planarization process, wherein pressing against the wafer includes expanding the membrane at a predetermined pressure level to press the wafer against the first surface of the polishing pad, the predetermined pressure level being between about 0.5 pounds-force per square inch and about 3 pounds-force per square inch. In one embodiment, the operation of generating the vibration includes: the method includes generating vibration at a first vibration frequency during a main polishing step of the chemical mechanical planarization process, generating vibration at a second vibration frequency less than the first vibration frequency during a polish-up polishing step during the chemical mechanical planarization process, and generating vibration at a third vibration frequency less than the second vibration frequency during a de-chuck step during the chemical mechanical planarization process. In one embodiment, the generating the vibration includes generating a first vibration pulse and a second vibration pulse separated from the first vibration pulse by a vibration-free time period, wherein a first amplitude of the first vibration pulse is different from a second amplitude of the second vibration pulse.

According to yet other embodiments of the present disclosure, there is provided a method of performing a chemical mechanical planarization process, comprising: holding a wafer by a retaining ring attached to a carrier, pressing the wafer against a first surface of a polishing pad, the polishing pad rotating at a first speed, dispensing a slurry onto the first surface of the polishing pad, and generating vibrations at the polishing pad.

In one embodiment, the operation of generating vibrations includes generating vibrations having a vibration frequency between about 10 kilohertz and about 50 kilohertz using a megasonic generator attached to the carrier, the megasonic generator including a piezoelectric transducer. In one embodiment, the first speed is between about 30 revolutions per minute and about 120 revolutions per minute, and the method further comprises rotating the carrier at a second speed between about 30 revolutions per minute and about 120 revolutions per minute. In one embodiment, the generating vibration includes generating vibration having a first vibration frequency during a first phase of the chemical mechanical planarization process and generating vibration having a second vibration frequency different from the first vibration frequency during a second phase of the chemical mechanical planarization process.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

1. A chemical mechanical planarization tool, comprising:

a carrier;

a retaining ring attached to the carrier and configured to hold a wafer during a chemical mechanical planarization process; and

a megasonic generator attached to the carrier and configured to generate vibrations during the chemical mechanical planarization process.